Simulations of realistic granular soils in oedometer tests using physics engine

Abstract

Summary Discrete element method (DEM) has become a preeminent numerical tool for investigating the mechanical behavior of granular soils. However, traditional DEM uses sphere clusters to approximate realistic particles, which is computationally demanding when simulating many particles. This paper demonstrates the potential of using a physics engine technique to simulate realistic particles. The physics engines are originally developed for video games for simulating physical and mechanical processes that occur in the real world to produce realistic game experiences. The simulation accuracy and efficiency of physics engines have been significantly improved in the last two decades allowing them to be used as a scientific tool in many disciplines. This paper introduces modeling methodologies of physics engine including realistic particle representation and the contact model. Then, oedometer tests are simulated using realistic particles scanned by X‐ray computed tomography (X‐ray CT). The simulation results agree well with experimental results. This paper demonstrates that physics engines can output contact parameters for geotechnical analysis and force chains for visualization.

General friction law for velocity‐stress dependent phase transition in granular flow

“…This simulation system for granular materials is a fork of the 3D creation suite Blender 67 and the physics engine Bullet 68 . For an efficient simulation of rigid particles, the Young's modulus and Poisson's ratio can be neglected by employing the impulse‐based dynamics (IBD), which have been well validated and verified 69–71 . The deformation and overlapping of particles are eliminated during the iteration procedure thus the elastic energy is zero in IBD method.…”

“…A set of parameters with the restitution coefficient of 0.8, the friction coefficient of 0.5, the transitional damping of 0.1, and the rotation damping of 0.05 are used for a slight damping system 33,56,66 . A small timestep of $$1/4000$$s is used to minimize overlapping of particles 70,72 . The granular assembly as shown in Figure 1C is first consolidated under a normal stress ($$P$$= 1, 10, 100, 1000 Pa).…”

“…68 For an efficient simulation of rigid particles, the Young's modulus and Poisson's ratio can be neglected by employing the impulse-based dynamics (IBD), which have been well validated and verified. [69][70][71] The deformation and overlapping of particles are eliminated during the iteration procedure thus the elastic energy is zero in IBD method. A consistent time step could be adopted for various flow states without worrying the numerical instability.…”

“…33,56,66 A small timestep of 1∕4000s is used to minimize overlapping of particles. 70,72 The granular assembly as shown in Figure 1C is first consolidated under a normal stress (𝑃= 1, 10, 100, 1000 Pa). Then, the assembly is subjected to shear deformation by moving the top plate with a speed V(𝑉=1 × 10 −2 -1 × 10 2 mm/s).…”

The role of particle shape in computational modelling of granular matter

“…Notably, GJK has been adopted widely in physics engines for computer graphics. Recently, physics engines such as PhysX 86 and Bullet 87 have become increasingly popular in scientific computation. For event-driven DEM or MD, it is non-trivial to predict the collision time for non-spherical moving particles 88 .…”